Among the naturally occurring contaminants in NGL pipelines is hydrogen sulfide which frequently attacks the interior surface of the pipeline thereby forming particulate iron sulfide. It is difficult to remove these particles from the NGL because many of them are in the micron size range. One of the methods used for removal of these particles is to contact the NGL stream with an aqueous wash liquid thereby forming a mixture having a hydrocarbon phase in which an aqueous phase is highly dispersed as droplets. This mixture is passed through an electrostatic precipitator wherein the particulate matter is drawn with the coalescing water droplets to the lower portion of the vessel (with the aid of gravity to the bottom of the vessel) while the hydrocarbon phase rises to the upper portion of the vessel. The purified hydrocarbon phase is removed from the vessel and passed on to further processing while the aqueous phase is removed from the vessel and filtered to remove the particulate contaminants. At least a portion of the water from which the particulates have been removed is recycled to the process as wash liquid.
Unfortunately, iron sulfide is soluble in water. A sufficient amount of iron sulfide is dissolved in the aqueous wash liquid and a sufficient amount of the wash liquid is entrained in the hydrocarbon effluent from the electrostatic precipitator that, due to changes in the operating conditions downstream of the precipitator, iron sulfide precipitates in apparatus downstream of the precipitator. The process and apparatus described above is set out in U.S. Pat. No. 4,370,236, the disclosure of which is incorporated here by reference. Decreasing the amount of dissolved iron sulfide in the hydrocarbon effluent from the electrostatic precipitator is the problem solved by the process of this invention.